Detecting salt water intrusion



C. S. SANDERS DETECTING SALTy WATER INTRUSION Filed Aug, 5o, 1941 2 sheets-sheet 14 3 .o o 6 H 2X 4 5%, o 5 a 6 y 6 w W vf, 3 FOV l @WI l lllllllllllllllllllllllllllllllllllllllllllllllll I,

June 26, 1945.V c'. s. v@ANDERS -DETECTING SALT WATER INTRUSION Filed Aug. so, 1941 2 Sheets-Sheet 2 r 1M W e ggm/za/e/ '5 pmi Puff-n 15101 l' various types. l

ful because no good method of determining per- Patented June 26, 1945 o 2,379,103 DElfCTING SALT WATER INTRUSION Clyde S. Sanders, TulsafOkla., assignor to Stanolind Oil and Gas Company, Tulsa, Okla., a corporation of Delaware 'Application Aurusc so, 1941, serial Nn. 409,057

(ci. irs-isz) 7 Claims.

This application relates to the art of detect- `ing the presence of inflow of water in wells and more particularly to the determination of the zoneI or zones of ingress of water into wells.

While this invention has particularly to do with the determination yof ingress of water into oil and gas wells, it is not so limited.

In the operation of wells to produce various kindsof valuableiproducts orin the drillingof test wells. to determine the presence of such products it is often found that water enters these wells in more or less profusion from one ormore permeable formations. Normally it is highly desirable to eliminate this water so that the substance being produced can be obtained at the well head with minimum dilution. This becomes of extreme economic importance in such matters as the operation of oil wells in which, unless considerable precautions are used, often the flow of oil from the well is not over a 'few percent of the 20 total fluid produced. This problem occurs not only in wells from which the production has been almost exhausted, but also in the early prolduction periods of wells and, in fact, may be a considerable problem as soon as a well is drilled.

Considerable ingenuity has been employed in` devising various means to shut orf the flow of water. In recent years these methods have progressed to such a point that it is possible to shut ofi. selectively various formations, for example, by the use of stage cement jobs and the like. However, it is obvious that the successful employment of any such method of shutting ofi' the flow of water must be based upon the knowledge of the location of thewater now with considerable exactitude. For example, if a well is producing from two formations it is Just as possible that Awater flowing into the well may come from the upper formation as from the lower;

Various methods have been employed in order to determine the zone or zones of water ingress into a well. Thus, for example, attempts have been made to utilize the data obtained from cores of the formations, i. e. by the location of permeable water sands. lAttempts have also been made with somewhat greater success, to utilize the information gained from electrical logs of However, this is oftenunsuccessmeability of the formations'has as yet been -set out and because the resistivity of a freely flowing water sand may be quite vsimilar to thatl of a relatively impervious low` resistance formation. Again, the effect of the infiltration of the fluid from the drilling mud into the various formations greatly affects the resistlvities obtained so that a highly permeable oil sand may show thel same electrical characteristics as a highly per"- meable water sand.

The best method of determination of the presence of water ingress into a well would seem to be the direct method, i. e. the detection of the water in the well as or justafter ithas seeped from the formation. In the past inventors have sought to determine the presence of this water kin the well by various electrical sounding methods which in general involve measuring the resistivity of the fluid column in the well as a function of depth, but these attempts have been usually unsuccessful because the dropping of the sounding apparatus into the well disturbs the column of liquid and.; tends-to spread out the water into Aa. zone of considerable extent which, of course, causes erroneous results to be obtained.

I have discovered a method of determining the location of-water ingress into a well which is simple, direct and expeditious, which involves only a single record and which can be carried out in any well regardless of the previous history of the wells operation. `It may be `applied to the determination Lof multiple points of ingress of water into the well as well as a single point of ingress. It is therefore an object of this invention to provide a method and apparatus for the determination of the location of water entering into a well.

It is a further object oi' this invention to providea method and apparatus for the determination of water ingress into a weil by means of which single electrical indication of the composite effects of water ingress at all points in y electrical indication is produced at the surface .fication and made a part thereof which illustrate embodiments of my invention. It is to be understood, however, that there aro further unillustratd embodiments of my invention which will be obvious to those skilled in the art, and that I do not intend to be limited to the embodiments y illustrated. In these drawings the same number 8 in various ilgures refers to the same or corresponding parts. I

Figure l is a diagrammatic representation of a cross section through a portion of the earth penetrated by a well and certain items oi' equipment l0 illustrating one embodiment oi' this invention;

and

Figure 2 illustrates the same cross section of the earth and' well shown in Figure 1 with another set oi equipment illustrating. an embodilo ment of my invention Figure 3 shows a cross section across one form oi electrode station adapted for use in my invention.

In Figure 1 of this application I have shown a zo diagrammatic cross section of a portion of the earth's surface traversed by a well II extending from the surfaceot the earth I2. This well has penetrated in turn an oil stratum Il, a water stratum Il, an impervious stratum I 5, an oil 2g stratum I B, and a water stratum I1. As shown in the drawings, two strings of casing have been set in the well. a surface string Il and a producltion string Il. the lower end of which is above the producing section of the well, i. e. the well section 30 from which well iiuids are obtained. In this case this section extends through the uncased portion of the well from the upper oil producing stratum Il' to the water stratum I1. At the surface, a conventional casing head indicated gena5 erally at 20 has been Provided. If the well is a ilowing wellfan oil saver or stuiling box` 2| is iitted on the casinghead, through which a cable 22l may bey lowered without substantial loss of well pressure. If the well is not ilowing no auch 40 equipment need be used. 'Ihe production string oi' casing is connected through a valve 23 to a line 24 which may lead. for example, w the atmosphere or to an oil and gas separator, etc. All oi' this equipment with the exception of the cable i5 is entirely standard.

It-is presumed that it is .known that water isl being produced in the well. As a ilrst step in I shutting oil' this water. a string of tubing is lowered into the well (through the stufIing box if 50 one is used) until the lower end is adjacent the bottomof the producing section. and a conditionv ing `iluidis circulated in the well. This circulating fluid should be a liquid in the electrical resistivity of which diil'ers markedly from that of 55 salt water. and can, for example, be oil. drilling mud prepared i'rom f-resh water, fresh water. carbon tetrachloride or the like. It-should either have a sumicent specific gravity so that the pressure head in the well is at least equal to the for- 60 mation pressure or else extra pressure should be applied to itin a manner well known in this art.

so that during the .conditioning o: the well no fluid from the formations can have ingress into the well bore. lBy the circulation of the iluid a5 through the wellthe material originally present in the producing section at the start or the conditioning operation is'replaced by a relatively uniform column or fluid of substantially uniform l resistivity differing considerably from that of 70 the connate water. removed or at least a sufficient number of joints The circulating pipe is then ot this circulating pipe are removed so that the lowst end of this pipe is above the producing f see on.

While maintaining the hydraulic pressure 'on the producing section, ythe cable 22 is now lowered into the well. As shown in this figure. this is a two-conductor cable with each conductor suitably insulated. 'I'he cable is unreeled from a reel 2l and passes-over a measuring sheave 2l as it is placed in the well so that thev depth of' the lower end of this cable is known at all times by inspection of the depth counter 21 actuated by revolution of .the measuring sheave 2l. Other types of depth measuring instruments may be employed if desired.

At the lower end of the cable 22 are a number ot pair of electrodes exposed to the fluids in the well` In Figure 1 these are numbered from 2l to I1, respectively. Across pairs oi electrodes such as 2l and 28, l0 and Il, etc. lare connected electrical impedances which can, for example, be resistances 38 to 42. respectively, preferably insulated from the well fluids, though this is not essential. These pairs of electrodes are connected in series by insulated wires 43 to I8. respectively. The end electrodes are connected to the two cable conductors. While preferably the spacing between the electrodes forming a pair should be uniform, and while I prefer to have the spacing between adjacent pairs of electrodes to -be equal, neither one of these conditions is at all requisite and any desired spacing may be employed between the electrodes in a pair or between adjacent pairs of electrodes. able in the case of small flows of water to have the two electrodes in a pair such as the electrodes Y approximately one-quarter inch apart and placed approximately horizontally in the well. In this embodiment of my inventionl it is advantageous when operating in a cased well producing through perforations to insulate the outer edges of the well electrodes and the wires between adjacent pairs of .electrodesso that accidental shortcircuits by contact with the well casing are avoided.

One such assemblage of electrodes I2 is shown in Figure '3. Inl this figure two circular sections of .wire screen 60 and 6I are mounted on wire rings l2 and B3 respectively. These rings are in turn mounted on supporting metal spiders 8l and The spiders are separated by a, cylindrical piece of insulating material 66 within which is mounted impedance 61 furnished at the ends with metal ferrules 6B which make electrical connection between the impedance 61 and the spiders 6I and I5. The electrical. connectors Il and A4I are attached to the ends of the spiders. and 8B, for example by conventional set screws (not shown). The wire rings 62 and 83 are surrounded by rubber protectors 69 and 1U which insulate the electrodes from accidental short-circuiting.

At the surface the ends of the cable stored on reelA 2l `are brought out to a pair of slip rings 41 and 4B on a disk of insulating material 4l mounted upon one end oi' the reel. V'Iwo brushes Ill and Il bear upon the slip rings 41 .and l0 and are connected together through a source of poten- 76 tial such as, for example, a battery B2 and a cur- It is normally desirrent measuring device I which may bea' meter, an oscillograpnor other means oi' producing a visual indication oi' the ow o f current, i. e. the impedance of the circuit. Any other potential source such as an alternating current generator could be used in place oi' the battery I2. If an A. C. source is used, condense'rs or inductances can be used instead of the resistances Il to 42 described.

After the cable has been lowered so that the electrodes are spaced along opposite the producingsection, the well is caused to produce a small amount of iiuid from the various permeable formations by decreasing the well head pressure (for example by opening valve 23) if the well is a,

flowing well, or by hailing the well if it does not now. As soon as water from a water-producing formation such as formation Il or I1 is kpro duced into the well it dlsplaces the conditioning fluid in a relatively short period of time. The initial displacement occurs opposite the water producing formation or formations. Very shortly after this 'occurs the pair of electrodes nearest the water Aproducing formation are short circuited by the relatively low resistivity water from the formation. This immediately changes the total impedance in the series circuit made up of the well electrode configuration, the cable, and the equipment at the surface, and accordingly -changesthe reading of the meter .or whatever impedance measuring device is employed. At a short interval of time later the next pair of electrodes in the direction of flow in the water is similarly short-circulted, causing a second change in the reading of the meter, and so on. By this means the presence of water is detected, practically as soon as the water flow commences.

Preferably the impedances between the various pairs of electrodes are all of different magnitudes. Thus the change in current occasioned by the lshort circuiting of any one impedance will be different from that due to the short circuiting of any other impedance. `Iy observing the magnitude of the initial change in current it is possible, knowing the depth of the various electrodes in the well, to determine the point of initial water entry. If there is evidence that the water flow is from two or more formations. such as shown in Figure 1, and that two pairs of electrodes may be short-circuited simultaneously, the impedances are chosen so that the sum of any two of such impedances, and preferably any number of such impedances, is not equal to the value of any one impedance. In this case the change in current due to the short-circuiting of two or more impedances is different from that due to the short-circuiting of ,any one impedance andtheoperator canimmediately deduce the location of the two or more points of water entry. Any desired combination of impedances satisfying this condition can be used. One combination, for example, for theflveimpedances shown involves the use of impedances of 2,000, 4,000, ,8,000, 16,000 and 32,000 ohms, respectively. In the case shown, using these impedances, one of the nrst two impedances snorted' out is impedance l2 which causes a decrease in the total impedance 0f the series circuit of 32,000 ohms. The other of the nrst two impedances shorted out is lmpedance 39 which vcauses a' decrease in the total series impedance of an additional 4,000 ohms. If the impedances are simultaneously short-circuited there is a total change of 36,000 ohms `'which results in a change in current which can not be mistaken for that due to the snorting out of yeither the 4,000 or the 32,000 ohm impedance a relativelyl low resistivity compared to that of Vconditioning fluid is of extremely high resistivity,

for example oil, since it is obvious that at all times the fluid between adjacent electrodes furnishes a path for electric current whichjis in'vparallel ...with that of the corresponding impedance. If

the -conditloningiluid is water, it normally. has

' oil, for example, vand in such `case much lower resistances or impedances should be used in the cable circuit. In one instance where the condi'- Itioning fluid had a resistivity of approximately 2500 ohm-inches and the salt water in the well was known to have a resistivity of approximately 12 ohm-inches, the following'set of circuit impedances could be advantageously employed on a four-zone determination: l10.5, 22.2; 50, 133. The effective impedance across each pair of ad- Joining electrodes, such as electrodes 28 and 29 in Figure 1, taking into account the effect of the conditioning water, becomes in this case, 10, 20, 40 and 80 ohms respectively. When the well fluid forms la low impedance path across the top pair of electrodes, for example, this impedance changes from 10 ohms to slightly less than l ohm, thus causing a total change in impedance of the entire circuit of approximately 9 ohms or a percent change in the current in the circuit of 6%.

If the operator is interested in determining the change in water level with time he merely observes the change in the metered current with time since each change in current is uniquely related upon the particular pair or' sets of pairs of electrodes that are short-circuited. If an oscillograph is used to record the current changes this record can be read in the same manner as the needle of the meter 53 can be observed, i. e. as a function of time.

If for any reason the spacing between pairs of electrodes is so great that the observer wishes to determine the location of the points -of water entry closer than this spacing, the well is reconditioned and the electrodes are again located in the well, this time at a different position, prefer-y ably opposite the mid points between the locations of the previous observation, and again a single reading of the composite effect at all electrodes is made in the manner already described. 'I'he location of the points of water ingress, therefore, should be located with whatever degree of precision is required. l

In Figure 2 I have shown an alternative set of equipment by means of which `the biggest ow ci' water into the well can be determined. In this case a single conductor insulated cable is employed. The lower end of this cable terminates in a :bare resistance wire 55 at the endof which can suitably be provided a weight 56 t0 stretch it the full length of the hole. Only a single slip ring 5l 'is employed and a single corresponding brush 58. The single brush 58 is connected in series with the meter 53 an-d a source of potential here shown as an alternator 59 to a ground connection B0. If desired a volt meter 6I can be connected across the source of potential, as shown.

The `resistance wire 55 is lowered into the well opposite the producing section after it has been conditioned and then the well is allowed to produce as before. The greatest source of water will cause the initial short circuit from the formation to a point on the resistance wire 5l. The point at which the resistance wire' l5 is short-circuited will hence depend upon the position inthe well of this wire and the position of the water sand. The total resistance in the circuit at the instant of initial current change will be the relatively negligible cable resistance, the resistance oi', the ground between the ground connection 60 and the water in the well, and the resistance of the non-short-circuited portion of the resistance wire 55. higher in resistance than-the other resistancesi'n the circuit, the total current immediately after the short-circuit will depend almost entirely upon Since this resistance wire is preferably much l the length of resistance wire above the point of contact with the salt water. By previous calibration, made, for example, by lowering the resistance wire 55 into a body of water, the current corresponding to a given length of non-short-cirl. cuited resistance wire can be determined.

Therefore the initial reading of the meter, oscillograph, or other current measuring device taken Vin connection with the known depth of the end of the cable, indicates the depth at which the short-circuit occurred. In Vcases where there is one main source of water this apparatus operates as well as that shown in Figure l and gives a result which is usually equally accurate as tothe depth of the body of' water.

It will be noted that in the employment of this invention it is unnecessary to make a large number of individual determinations of the resistivity of the electrode configuration in the well since one single indication is produced of the composite effects occurring-in the well. Likew'iseof interest is that the fact that the equipment in the Well is not moved during the time that the readings are being taken so that there is no Way by which electrode movement can spread out the flow oi' water into a zone which would obscure the sharpness of the determination of the water zone or zones. Y

Various modifications and adaptations oi my invention will be apparent to those skilled in the art. The inherent novelty in this invention is best set 4forth in the appended claims.

I claim:

1. In apparatus for determining the location of atleast one zone of water ingress into a well including means for displacing the fluids in said well by a conditioning fluid, an electric characteristic of which differs from the same characteristic of said water, an electric cable adapted to be lowered into said well, means for determining the depth of the lower end ofA said cable in said well, and means for permitting ingress of water into said well after the lower end of said cable has been disposed in the region to be investigated in said well, the improvement corn prising a series-connected group of alternate impedances and connectors of considerable length, the ends or which Agroup are connected to two conductors ofysaid cable. each impedance in said group being of different value from that of any/other impedance in said group and from any combination of said impedances, a plurality of pairs of electrodes equal innumber to the nurnber of said impedances, the electrodes of each pair being connected to the opposite ends of only one of said impedances, a source of potential, means for applying said source across the upper terminals of said cable, and means inserted in said circult'including said' source, said cable, and

said impedances for producing a visible indication or the flow oi' electriccurrent in said circuit. 2. Apparatus for well logging according to claim 1 in which the electrodes oi each of said pairs of electrodes are separated by a distance of from one-quarter to six inches and the separation between adjacent impedances is between two and twenty feet.

3. In a method for determining the location of a zone ofwater ingress through a permeable formation traversed by a well in which the i'iuidsv in a portion oi said well including the region traversing said formation are displaced by a conditioning fluid,r an electrical; characteristic of which is different troni the same characteristic of the water insaid formation, so that the ingress oi' well fluids into-said well is temporarily halted.

in which a plurality of stationary duid character l measuring zones substantially vertically displaced yfrom each other are established at known depths within said well inthe vicinity of said formation and in which formation fluids are caused to flow Y into said welll the improvement comprising producing an electrical effect at each of said zones, so varying said effect upon the ing-resa of formation water into said zone, that each of said effects. regardless of the conductivity of said water, is'of different magnitude from that produced' at any other of said zones and different from the simultaneous resultant of any plurality of said effects, varying the current in a single electrical circuit as the simultaneous resultant of the electrical .effects at all of said zones. and producing a visualV indication directly related to said variation insaid current.

4. In apparatus for determining the location of a zone of salt water ingress into a. well including means for stopping the ingress of fluids into said well and for displacing such fluids as are present in the producing section of said well by a conditioning fluid, means for lowering a testlngapparatus in said well, means for'determining the depth of said apparatus in said well and means for causing ingress of well fluids into said well, the improvement in which said apparatus' comprises a plurality of substantially vertically spaced pairs of well fluids, a similar plurality of impedancesv each of which is connected across one of' said pairs of electrodes, the value of each impedance being different from the value of all other impedances and from the sums of any plurality of other impedances in said circuit, a plurality of conductors so connecting one electrode of each pair to an electrode of an adjacentY pair as to connect said impedances in series with each other to form a single series circuit, an electric cable two conductors of which are connected to the opposite ends, respectively, of said plurality of pairs of electrades, and means located at the surface of the' earth for producing a visual indication of the `change in impedance of the series circuit including said cable and said impedances due to the 'formation of at least one low-resistancepath across at least one of said impedances by ingress of salt water into said well.

5. In apparatus for determining the location of a zone of `water ingress through a permeable formation traversed by a well including means for displacing the fluids in a portion of said well including the region traversing said formation by a conditioning fiuid an electrical characteristic of which is different from the same characteristic of the water in said formation so that the ingress of well fluids into said well is temporarily halted,

means for disposing test apparatus in said well in a ilxed position and at a known depth and in the vicinity oi said formation, and means for causing ingress of well fluids into said well. the improvement in which the test apparatus-comprises a plurality of electric fluid character-measuring stations each adapted to produce a change in an electric characteristic thereof upon the presence oi' water thereat, each of said stations having its characteristics so designed as to produce a change, the magnitude of which differs from the magnitude of the change at each of said other stations and from the magnitude of the sum or any plurality of changes at saidl other stations, a source of potentiaL'current indicating means, and means for connecting in a single series circuit all of said stations, said source, and said indicating means, whereby the electric eiiect producedat each iluid character-measuring station changes upon arrival of water at said station, thus varying the f indication of said indicating means.

8. Apparatus:l forv determining Vthe location of changes in the electrical conductivity of iiuids at various points along theA length of an oil well comprising a simple series electric circuit including one indicating means and a part which extends intothewell andisadaptedtoberaisedand lowered therewithin, said part of said circuit inchidinginseriesconnecticnatleasttwoimpedcups s SANDERS.

ances and'means electrically exposed to the well liiuin'is at the ends of said impedances, said impedances having such different values that whenever one or more of said impedances are shunted by the presence oi 4any conductive uid which forms a low resistance path between thevexposed means at the ends of said one or more shunted impedances, the identity of said one or more shunted impedances can be determined from said one indicating means.

7. A method for determining the location of changes in the electrical conductivity of fiuidsat various points along the length of an oil well comprising producing an electrical eiIect at each of a plurality of iiuid character measuring zones in said well, so varying said eiect upon the presence of a conductive fluid at each oi said zones that each of said eiects, regardless of the conducuvityof said conductive nuid, is of different magnitude from that produced at any other of said zones and different from the simultaneous resultant of any plurality of said effects, varying the currentv in a single electrical circuit as the simultaneous resultant of the electrical effects at all of said zones. and producing a visual indication directly related-to said .variation in said current.

CLYDE S. SANDERS.

Ii:-i'e-herre'la'y'` certified that error appears inthe. printed specification .patent requiring correction as follows: Page h., second cclunngline k7', claim'ii., after. "paire of" insertI the words ,e1ec

treden' fringed for .exposure te contact bye-g 'andi-that the said Letters Patent shovulciberead'withV this correctionthereiny that the same may ccn- Arom. so merecer-alor sns use v1n the' Patent office. 'Signed and sealed. this 18th day of September, A. D. '19145.

(Seal) I Leslie 'Y Frazer First Assistant Commissioner of Patents.

means for disposing test apparatus in said well in a ilxed position and at a known depth and in the vicinity oi said formation, and means for causing ingress of well fluids into said well. the improvement in which the test apparatus-comprises a plurality of electric fluid character-measuring stations each adapted to produce a change in an electric characteristic thereof upon the presence oi' water thereat, each of said stations having its characteristics so designed as to produce a change, the magnitude of which differs from the magnitude of the change at each of said other stations and from the magnitude of the sum or any plurality of changes at saidl other stations, a source of potentiaL'current indicating means, and means for connecting in a single series circuit all of said stations, said source, and said indicating means, whereby the electric eiiect producedat each iluid character-measuring station changes upon arrival of water at said station, thus varying the f indication of said indicating means.

8. Apparatus:l forv determining Vthe location of changes in the electrical conductivity of iiuids at various points along theA length of an oil well comprising a simple series electric circuit including one indicating means and a part which extends intothewell andisadaptedtoberaisedand lowered therewithin, said part of said circuit inchidinginseriesconnecticnatleasttwoimpedcEn'rIFIcATE orL connection.

cups s SANDERS.

ances and'means electrically exposed to the well liiuin'is at the ends of said impedances, said impedances having such different values that whenever one or more of said impedances are shunted by the presence oi 4any conductive uid which forms a low resistance path between thevexposed means at the ends of said one or more shunted impedances, the identity of said one or more shunted impedances can be determined from said one indicating means.

7. A method for determining the location of changes in the electrical conductivity of fiuidsat various points along the length of an oil well comprising producing an electrical eiIect at each of a plurality of iiuid character measuring zones in said well, so varying said eiect upon the presence of a conductive fluid at each oi said zones that each of said eiects, regardless of the conducuvityof said conductive nuid, is of different magnitude from that produced at any other of said zones and different from the simultaneous resultant of any plurality of said effects, varying the currentv in a single electrical circuit as the simultaneous resultant of the electrical effects at all of said zones. and producing a visual indication directly related-to said .variation in said current.

CLYDE S. SANDERS.

Ii:-i'e-herre'la'y'` certified that error appears inthe. printed specification er ensissie gember-.ed

.patent requiring correction as follows: Page h., second cclunngline k7', claim'ii., after. "paire of" insertI the words ,e1ec

treden' fringed for .exposure te contact bye-g 'andi-that the said Letters Patent shovulciberead'withV this correctionthereiny that the same may ccn- Arom. so merecer-alor sns use v1n the' Patent office. 'Signed and sealed. this 18th day of September, A. D. '19145.

(Seal) I Leslie 'Y Frazer First Assistant Commissioner of Patents. 

